PROJECT SUMMARY/ABSTRACT Despite the enormous success of the World Health Organization's Expanded Programme on Immunization, which has saved millions of lives over the past 44 years, infectious disease remains the second leading cause of death worldwide.1-4 Of the 15 million deaths that occur each year, 10% are vaccine-preventable, yet continue to occur due to the logistical challenges associated with administering multiple injections over the course of months in low-resource settings.5 The remaining 90% of deaths cannot be prevented with existing vaccines and will likely require the development of highly immunogenic vaccines against key disease targets.6,7 For example, RTS,S/AS01 (MosquirixTM), the only clinically-approved malaria vaccine, is effective in just 26% of young children after 3 doses and 39% of children after 4 doses.8 Although additional doses may further improve seroconversion rates, there are limits to economic and societal tolerance for additional doses.9 Instead, strategies that enhance antigen immunogenicity may be able to: (1) achieve similar levels of seroconversion after fewer doses, (2) improve seroconversion rates after the same number of doses, and/or (3) enable the use of subunit vaccines that are typically safer and more stable, but inherently less immunogenic.10 In addition to addressing a clear clinical need in the developing world, this strategy is also relevant for the developed world, especially for human papillomavirus (HPV) and meningitis vaccines, which require multiple doses, but are subject to low initial compliance (one-dose coverage of 66% and 85% in the U.S., respectively) and high drop-out rates (25% and 52% of individuals that receive one dose do not receive a second).11-13 My postdoctoral research has primarily focused on the development of a single-injection vaccination platform that uses biodegradable microparticles to release antigen in discrete pulses that mimic multiple injections. This proposal builds off of my previous work and aims to not just replicate the immunogenicity of multi-injection immunization regimens, but enhance vaccine immunogenicity using three timed or targeted vaccine delivery strategies. The first approach will develop a vaccine delivery platform that uses ultrahigh resolution 3D printing to fabricate surface-eroding microparticles that exhibit well-controlled release kinetics and protect antigen from harmful environmental factor. Because optimal vaccine release kinetics have yet to not been identified,14 these devices will also be used to determine favorable release profiles. The second approach will create dissolvable microneedle patches for the intradermal delivery of controlled release vaccines. By leveraging the high concentration of dendritic cells in the skin and benefits of delayed release, these formulations may be able to enhance vaccine immunogenicity while offering other advantages such as improved antigen stability, reduced pain, and the potential for self-administration. The third strategy presented in this proposal will explore the use of in situ-forming hydrogels that self-assemble in the lymph node and release vaccine over time to prolong antigen residence time and exposure to nave B cells.